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feat: update the downloading lesson of the JS2 course to be about JavaScript #1657

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170 changes: 102 additions & 68 deletions sources/academy/webscraping/scraping_basics_javascript2/04_downloading_html.md
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Expand Up @@ -12,61 +12,83 @@ import Exercises from './_exercises.mdx';

---

Using browser tools for developers is crucial for understanding the structure of a particular page, but it's a manual task. Let's start building our first automation, a Python program which downloads HTML code of the product listing.
Using browser tools for developers is crucial for understanding the structure of a particular page, but it's a manual task. Let's start building our first automation, a JavaScript program which downloads HTML code of the product listing.

## Starting a Python project
## Starting a Node.js project

Before we start coding, we need to set up a Python project. Let's create new directory with a virtual environment. Inside the directory and with the environment activated, we'll install the HTTPX library:
Before we start coding, we need to set up a Node.js project. Let's create new directory and let's name it `product-scraper`. Inside the directory, we'll initialize new project:

```text
$ pip install httpx
$ npm init
This utility will walk you through creating a package.json file.
...
Successfully installed ... httpx-0.0.0
```

:::tip Installing packages

Being comfortable around Python project setup and installing packages is a prerequisite of this course, but if you wouldn't say no to a recap, we recommend the [Installing Packages](https://packaging.python.org/en/latest/tutorials/installing-packages/) tutorial from the official Python Packaging User Guide.

:::
Press ^C at any time to quit.
package name: (product-scraper)
version: (1.0.0)
description: Product scraper
entry point: (index.js)
test command:
git repository:
keywords:
author:
license: (ISC)
# highlight-next-line
type: (commonjs) module
About to write to /Users/.../product-scraper/package.json:

{
"name": "product-scraper",
"version": "1.0.0",
"description": "Product scraper",
"main": "index.js",
"scripts": {
"test": "echo \"Error: no test specified\" && exit 1"
},
"author": "",
"license": "ISC",
# highlight-next-line
"type": "module"
}
```

Now let's test that all works. Inside the project directory we'll create a new file called `main.py` with the following code:
The above creates a `package.json` file with configuration of our project. While most of the values are arbitrary, it's important that the project's type is set to `module`. Now let's test that all works. Inside the project directory we'll create a new file called `index.js` with the following code:

```py
import httpx
```js
import process from 'node:process';

print("OK")
console.log(`All is OK, ${process.argv[2]}`);
```

Running it as a Python program will verify that our setup is okay and we've installed HTTPX:
Running it as a Node.js program will verify that our setup is okay and we've correctly set the type to `module`. The program takes a single word as an argument and will address us with it, so let's pass it "mate", for example:

```text
$ python main.py
OK
$ node index.js mate
All is OK, mate
```

:::info Troubleshooting

If you see errors or for any other reason cannot run the code above, it means that your environment isn't set up correctly. We're sorry, but figuring out the issue is out of scope of this course.
If you see `ReferenceError: require is not defined in ES module scope, you can use import instead`, double check that in your `package.json` the type property is set to `module`.

If you see other errors or for any other reason cannot run the code above, it means that your environment isn't set up correctly. We're sorry, but figuring out the issue is out of scope of this course.

:::

## Downloading product listing

Now onto coding! Let's change our code so it downloads HTML of the product listing instead of printing `OK`. The [documentation of the HTTPX library](https://www.python-httpx.org/) provides us with examples how to use it. Inspired by those, our code will look like this:

```py
import httpx
Now onto coding! Let's change our code so it downloads HTML of the product listing instead of printing `All is OK`. The [documentation of the Fetch API](https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API/Using_Fetch) provides us with examples how to use it. Inspired by those, our code will look like this:

url = "https://warehouse-theme-metal.myshopify.com/collections/sales"
response = httpx.get(url)
print(response.text)
```js
const url = "https://warehouse-theme-metal.myshopify.com/collections/sales";
const response = await fetch(url);
console.log(await response.text());
```

If we run the program now, it should print the downloaded HTML:

```text
$ python main.py
$ node index.js
<!doctype html>
<html class="no-js" lang="en">
<head>
Expand All @@ -80,15 +102,15 @@ $ python main.py
</html>
```

Running `httpx.get(url)`, we made a HTTP request and received a response. It's not particularly useful yet, but it's a good start of our scraper.
Running `await fetch(url)`, we made a HTTP request and received a response. It's not particularly useful yet, but it's a good start of our scraper.

:::tip Client and server, request and response

HTTP is a network protocol powering the internet. Understanding it well is an important foundation for successful scraping, but for this course, it's enough to know just the basic flow and terminology:

- HTTP is an exchange between two participants.
- The _client_ sends a _request_ to the _server_, which replies with a _response_.
- In our case, `main.py` is the client, and the technology running at `warehouse-theme-metal.myshopify.com` replies to our request as the server.
- In our case, `index.js` is the client, and the technology running at `warehouse-theme-metal.myshopify.com` replies to our request as the server.

:::

Expand All @@ -110,28 +132,30 @@ First, let's ask for trouble. We'll change the URL in our code to a page that do
https://warehouse-theme-metal.myshopify.com/does/not/exist
```

We could check the value of `response.status_code` against a list of allowed numbers, but HTTPX already provides `response.raise_for_status()`, a method that analyzes the number and raises the `httpx.HTTPError` exception if our request wasn't successful:
We could check the value of `response.status` against a list of allowed numbers, but the Fetch API already provides `response.ok`, a property which returns `false` if our request wasn't successful:

```py
import httpx
```js
const url = "https://warehouse-theme-metal.myshopify.com/does/not/exist";
const response = await fetch(url);

url = "https://warehouse-theme-metal.myshopify.com/does/not/exist"
response = httpx.get(url)
response.raise_for_status()
print(response.text)
if (response.ok) {
console.log(await response.text());
} else {
throw new Error(`HTTP ${response.status}`);
}
```

If you run the code above, the program should crash:

```text
$ python main.py
Traceback (most recent call last):
File "/Users/.../main.py", line 5, in <module>
response.raise_for_status()
File "/Users/.../.venv/lib/python3/site-packages/httpx/_models.py", line 761, in raise_for_status
raise HTTPStatusError(message, request=request, response=self)
httpx.HTTPStatusError: Client error '404 Not Found' for url 'https://warehouse-theme-metal.myshopify.com/does/not/exist'
For more information check: https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/404
$ node index.js
file:///Users/.../index.js:7
throw new Error(`HTTP ${response.status}`);
^

Error: HTTP 404
at file:///Users/.../index.js:7:9
at process.processTicksAndRejections (node:internal/process/task_queues:105:5)
```

Letting our program visibly crash on error is enough for our purposes. Now, let's return to our primary goal. In the next lesson, we'll be looking for a way to extract information about products from the downloaded HTML.
Expand All @@ -151,13 +175,15 @@ https://www.aliexpress.com/w/wholesale-darth-vader.html
<details>
<summary>Solution</summary>

```py
import httpx
```js
const url = "https://www.aliexpress.com/w/wholesale-darth-vader.html";
const response = await fetch(url);

url = "https://www.aliexpress.com/w/wholesale-darth-vader.html"
response = httpx.get(url)
response.raise_for_status()
print(response.text)
if (response.ok) {
console.log(await response.text());
} else {
throw new Error(`HTTP ${response.status}`);
}
```

</details>
Expand All @@ -176,26 +202,30 @@ https://warehouse-theme-metal.myshopify.com/collections/sales
Right in your Terminal or Command Prompt, you can create files by _redirecting output_ of command line programs:

```text
python main.py > products.html
node index.js > products.html
```

If you want to use Python instead, it offers several ways how to create files. The solution below uses [pathlib](https://docs.python.org/3/library/pathlib.html):
If you want to use Node.js instead, it offers several ways how to create files. The solution below uses the [Promises API](https://nodejs.org/api/fs.html#promises-api):

```py
import httpx
from pathlib import Path
```js
import { writeFile } from 'node:fs/promises';

url = "https://warehouse-theme-metal.myshopify.com/collections/sales"
response = httpx.get(url)
response.raise_for_status()
Path("products.html").write_text(response.text)
const url = "https://warehouse-theme-metal.myshopify.com/collections/sales";
const response = await fetch(url);

if (response.ok) {
const html = await response.text();
await writeFile('products.html', html);
} else {
throw new Error(`HTTP ${response.status}`);
}
```

</details>

### Download an image as a file

Download a product image, then save it on your disk as a file. While HTML is _textual_ content, images are _binary_. You may want to scan through the [HTTPX QuickStart](https://www.python-httpx.org/quickstart/) for guidance. You can use this URL pointing to an image of a TV:
Download a product image, then save it on your disk as a file. While HTML is _textual_ content, images are _binary_. You may want to scan through the [Fetch API documentation](https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API/Using_Fetch#reading_the_response_body) for guidance. Especially check `Response.arrayBuffer()`. You can use this URL pointing to an image of a TV:

```text
https://warehouse-theme-metal.myshopify.com/cdn/shop/products/sonyxbr55front_f72cc8ff-fcd6-4141-b9cc-e1320f867785.jpg
Expand All @@ -204,16 +234,20 @@ https://warehouse-theme-metal.myshopify.com/cdn/shop/products/sonyxbr55front_f72
<details>
<summary>Solution</summary>

Python offers several ways how to create files. The solution below uses [pathlib](https://docs.python.org/3/library/pathlib.html):
Node.js offers several ways how to create files. The solution below uses [Promises API](https://nodejs.org/api/fs.html#promises-api):

```js
import { writeFile } from 'node:fs/promises';

```py
from pathlib import Path
import httpx
const url = "https://warehouse-theme-metal.myshopify.com/cdn/shop/products/sonyxbr55front_f72cc8ff-fcd6-4141-b9cc-e1320f867785.jpg";
const response = await fetch(url);

url = "https://warehouse-theme-metal.myshopify.com/cdn/shop/products/sonyxbr55front_f72cc8ff-fcd6-4141-b9cc-e1320f867785.jpg"
response = httpx.get(url)
response.raise_for_status()
Path("tv.jpg").write_bytes(response.content)
if (response.ok) {
const buffer = Buffer.from(await response.arrayBuffer());
await writeFile('tv.jpg', buffer);
} else {
throw new Error(`HTTP ${response.status}`);
}
```

</details>
14 changes: 14 additions & 0 deletions sources/academy/webscraping/scraping_basics_javascript2/05_parsing_html.md
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Expand Up @@ -38,6 +38,20 @@ $ pip install beautifulsoup4
Successfully installed beautifulsoup4-4.0.0 soupsieve-0.0
```

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This is removed and addressed in subsequent commits of #1584, which are yet about to become Pull Requests.

:::tip Installing packages

Being comfortable around Python project setup and installing packages is a prerequisite of this course, but if you wouldn't say no to a recap, we recommend the [Installing Packages](https://packaging.python.org/en/latest/tutorials/installing-packages/) tutorial from the official Python Packaging User Guide.

:::

:::info Troubleshooting

If you see other errors or for any other reason cannot run the code above, it means that your environment isn't set up correctly. We're sorry, but figuring out the issue is out of scope of this course.

:::
-->

Now let's use it for parsing the HTML. The `BeautifulSoup` object allows us to work with the HTML elements in a structured way. As a demonstration, we'll first get the `<h1>` element, which represents the main heading of the page.

![Element of the main heading](./images/h1.png)
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